Gyroscopic compass



Aug. 30, 1938. w. G. HARDING Ef Al.

GYROSCOPIC COMPASS Filed May 13, 1936 4 Sheets-Sheet 2 Aug. 30, 1938. w.G.. HARDiNG ET Al.

GYRoscQPI coMPAss Filed May 1:5, 19:56

4 Sheets-Sheet 5 E .Il T L A Q. m N m 2: VN Q 2 VWQVMW 5. MM S Q7. @u myn: c. m2 Q ma R3 E R R .vw R E a n Eb mm o wn n E wm uw @mi y. www uw Mwww. W Hm 6m. w B E Wm n my W3 Aug. 30, 1938. w. G. HARDING ET A1.

I GYROSCOPIC COMPASS 4 Sheets-Sheet 4 Filed May 13, 1936 Patented Aug.3o, leas.

UNITED STATES VPATENT OFFICE GYROSCOPIC COMPASS l Application May 13,1936, serial No. 79,408 In Great Britain May 15, 1935 9 claims. (ci.33-226) This invention relatesv to gyroscopic compasses, andparticularly to means for correcting the readings of such compasses whenthey are carried on a moving vehicle such as a ship.

A gyro compass carried with the earth indicates the true north. This. isbecause the supports of the compass experience a rotation about an axisparallel to the earths axis. The gyro settles with its axis along thehorizontal projection of "his l0 axis of rotation of its supports-thetrue north. If, however, the compass is mounted on a moving vehicle,such as a ship, the motion imparted toits supports is not the *same asthat of the surface of the earth in its vicinity, but is made up of thismotion and of the motion of the ship over the earths surface. Thecompass supports are therefore subjected to a total or resultantrotation in space about some axis which is, in general, diii'erent fromthe axis of rotation 20. of the earth. The result is that the compasssettles with its axis along the horizontal proection of this axis oftotal rotation, instead of pointing to the true north. The errormeasured in the horizontal plane is called the speed error.

The present invention' relates to means for correcting the readings ofthe compass to compensate for this speed error. The subject matter ofthe present invention is similar to that disclosed in the prior UnitedStates Patent No.v

1,255,480, but the object of the present invention is to provide novelmeans for mechanically calculating and applying the correctionand forcalculatingl such vcorrectionaccording to a more accurate formula thanhas hitherto been used.

The formula usually accepted for the speed error may be expressed in theform L0 where E is the speed error, or the angle measured clockwise fromthe true north to the gyro axis.

C is the course angle of the ship measured clockwise from the truenorth. S is the speed of the ship over the earths surface. V is thecompo- 5 nent of the surface speed of the earth at the equator due tothe earths rotation about its f-axis .once Ain a sidereal daygand L isthe latitude of the ship.-

Disregarding signs and also the difference be- 0 tween an angle inradians .and its tangent, the

formula can be expressed in numerical form.

*Error in degrees=.0635 i knots cos C sec. L.

'-S cos C Vcos L-l-S sin C The incorrect formula makes it appear that.i'or a ship travelling at a given speed,4 the compass, error lisgreatest for courses due north and due south. The true formula showsthat the error is greatest for courses to the west of due north or duesouth. l

Broadly stated we provide according to the present invention meansformechanically calculating a correction according to the true formula asabove stated or to mathematical transformations of it. The resultsobtained therefore diiier from those obtained with previous correctorsin taking account of the second term of the denominator in the trueformula; they also differ in taking account of the differences between Eexpressed in radians and tan E. Both diierences, though small for smallcorrections, begin to assume importance when the correction angle islarge, as occurs with high speeds at high latitude.

The devices used in our invention are intended to be set, eithermanually or by automatic means not falling within the scope of theinvention, in accordance with the ships speed and latitude. Thereafterthe devices are automatic in the sense that when the ship changes coursethe correction is automatically changed in accordance with the formula.In order that the devices may be auto- '..matic in this sense they aresubjected to the action ofmembers. turning relatively to each otherthrough the same angle as the change of cdurse. Such relatively movingmembers are found naturally in the compass itself or in repeater com-` ypasses. The correction' when calculated by the devices of our inventionmay be used in any suitable part of the compass, or in repeatercompasses, or in a transmission system from the compass to repeaterCompasses.

More specifically stated, therefore, a feature of the present inventionis the provision of means operated from' a gyro compass or itsequivalent to calculate a correction according to the formula t E -S cosC .an Vcos L-l-S sinfC or to mathematical transformations of thisformula.

difference between the formula hitherto employed Another feature is themechanical application of a correction according to this formula to agyro compass or to repeater Compasses, or to transmitters.

A further feature is the provision of means adapted to make the speedcorrection given by the above formula unaiected by other correc` tionsgiven to a gyro compass. v

A still rurther feature is the provision of means adapted to providecorrections for the speed errors of a gyro compass or the like whichcorrectl in compass. correctors and the formula employed in the presentinvention.

Figure 2 is a diagram showing the geometrical principles employed in thepresent invention for calculating the correction.

AFigure 3 isA a sectional elevation of the upper part of a gyro compassembodying one form cf our invention, the section being taken along theline 3 8 of Figure 4. Figure 4 is a plan view of the same compass.Figure 5 is a part elevation showing more clearly some details of anadjustable slide used in the Acorrector device of Figures 3 and 4.

Figure 6 is a sectional elevation of the upper part of a compassincorporating another form of the invention, the section being taken onthe line 6-6 of Figure '1. l

Figure 7 is a plan view of this compass with the compass card in partbroken away to show details of the corrector mechanism.

Referring to Figure 1, OCP is a triangle of velocities. OC representsthat part of the velocity of a point on the earths surface in latitude Lwhich is due to the rotation of the earth about its axis once in asidereal day. A ship is supposed to be situated'at this point and tohave a velocity S relative to the earths surface, in the direction ofthe ships heading. This velocity is represented by CP.

The earths velocity OC is from west to east and is of magnitude V cos Lwhere Vl is the velocity of rotation of a point onthe earths equator.Theline CN perpendicular to OC therefore represents the true north andthe angle NCP is the course angle C of the ship. Y

The line OP which is the vector sum of OC and CP, therefore, representsthe resultant velocity of the ship over a non-rotating sphere coincidentwith the earth's surface. It makes the angle COP with the velocity OCdue to the earths rotation alone. A gyro compass indicates the resultantrotation to which it is vsubjected by virtue of the fact that it is onthe ship as well as on the earth, so that the axis of the gyro turns toa position perpendicular to OP instead of to a position perpendicular toOC.

The angle COP is therefore the speed error of the compass. The error isnaturally measured from the correct direction to the erroneous one, i.e., from OC to OP, and in the same sense in which course angles aremeasured, i. e., clockwise. It follows that whenever the course has apositive northerly'component as in Fig. 1 the error E is negative. .andthe angle COP, if measured anticlockwise, is -'E. For a course with apositive northerly component the gy-ro axis "has a negaaiaaesa are CP'and P'P. Previous correctors have neglected the easterly component andhave calculated the correction as if the ship had only the northerlycomponent velocity CP'. This velocity is S cos C'. Previous-correctoras,therefore.,

instead of being designed. to correct. the error COP, were designed to'correct the supposed error COP', or -E', which is given by the formula(Here the negative sign takes account of the fact that the angle COP inthe figure is .E.)

The correct formula is given by where PM is perpendicular to OC, so thatCM=S sin C.

Consequently vtan E= v -(z-j y In the methods herein shown formechanically calculating this .correction we set up, on some suitablescale a physical embodiment of the sides CP and OC of the velocitytriangle COP, and we maintain these sides in the correct angular andscale relationship as the ship changes its course. Thereby the angle COPmay be picked olf the mechanism and used for correction purposes.

l We may construct our physical embodiment to represent the velocitytriangleon the same scale in all latitudes, but we have only shown inthe drawings the method in which the scale of representation is changedwith latitude inA such a way that OC remains constant in all latitudes`The geometrical relationships are shown in Fig.

2. Here OC is taken of some fixed length indicated as unity, and CP onthe same scale is S Vcos L Clearly the triangle of Fig. 2 represents thetriangle of Figure l on a scale inversely asaV cos L. Figure 2 is drawnfor a northeast course of the ship, for which Figures 3 and 4 are alsodrawn, whereas Figures 6 and 7 are drawn for a course slightly west ofnorth. Incidentally in Figure 2 there is also shown the trlangleCOPa foraship travelling on a NW. course at the same speed as that for whichtriangle COP is drawn. This shows clearly the difference for the samespeed in the errors on a NW. course and on a NE.'course. ignored in theolder formula.

From Figures 1 and 2A it is evident that the angle OCP, between themembers that physically represent the vectors OC and CP, must be +Cwhere C is the course'4 angle measured from the true north and not fromthe gyro axis.

Referring to Figures 3 to 6, we will now describe the operation of somedevices in accordance with our invention as applied to one particulartype of compass. We start with an explanation of those features Vof thecompass, an understanding of which is necessary in order to `appreciatethe op-v eration of the devices.

In these figures, ,I is the main supporting frame of the compass. Thisframe is itself supported in gimbal rings (not shown) from a binnacle orsimilar structure fixed to the deck of the ship, so that It isdirectionally locked to the fore and aft line of the ship. v

Bearings 2, 2' are provided in this frame to support the inner orturning member of the compass with freedom of rotation about a verticalaxis. The inner member is shown as being of the type in which asensitive element is supported in a following or phantom element. `Thusin the gures, the gyroscope rotor case 3 is supported for oscillationabout a horizontal east-west axis (not shown) in a vertical ring i,whose plane is the east-west vertical plane.

The ring 4 hangs by a suspension 5 from parts supported by a stem 6solid with a ring 1, which is supported in turn in the bearings 2, 2'.To this ring 1 is attached a gear frame 3 on which are cut the teeth ofthe azimuth gear 9. Rigidly secured to the stem 6 is the hub I0 to whichis fixed the compass card Il carrying a scale of degrees. On this scalethe ships heading is read opposite a. lubber mark I2 on a lubber ringI3. The rim of this ring rests on the rim of the main compass frame I.The rim of the main frame I is supported on four radial-arms from, thecentre, and the rim of the lubber ring I3 is supported on four radialarms from its hub. 'I'his hub is mounted on bearings I4 on the mainframe, so that the lubber ring can rotate round a vertical axis on themain frame. Since the ships course is to read by the relative positionof the card I I and the lubber mark I2, it is important to observe howthis relative position is determined.

On the compass frame I is attached a motor I5 -which drives the azimuthgear 9 through gearing shown as I 6, I1, I8. This motor is controlled bysome system shown in Figure 6 as a contact wheel I9 on a member 2|mounted on the vertical ring 4. The contact Wheel runs over contacts 20carried on the phantom ring 1 whenever there is relative movementbetween the two rings. The motor I5 is thereby so controlled as alwaysto drive the gear 9 in the appropriate direction to make the plane ofthe phantom ring.1 coincide with that of the vertical ring l. Thecompass card II turns with the ring 1 and so is always in a xeddirectional relationship with the ring 4, and therefore with the axis ofthe gyro. 'I'he card is so marked out that 360 corresponds to the northend of the gyro axis.

From the above it is evident that the 360 mark will always be driveninto a position in space corresponding to the direction of the gyroaxis, and it will therefore be subject to the speed errors ofthegyroitself. Thus, if the ship is proceeding on a course with a northerlycomponent, the 360 mark will not be due north of the compass centre butwill be displaced anti-clockwise to the west. In

order lto be able to read the true course as measured fromv the truenorth instead of from the 360 mark on the card, the lubber mark mustalso be displaced anti-clockwise by the same amount. This is broughtabout by a rotation of the lubber ring as a whole by the correctormechanism.

All the above is already knownand forms' no part'of the subject matterof our invention. Our

invention is concerned with a corrector mechanism which can be used,inter alia, to act as. the corrector for the above type of compass so asto displace the lubber ring I3 on the main frame I by an amount equal tothe correction angle.

y How. ever, it must not be supposed that our invention is restricted tothe application of correction by displacing the lubber ring.

It may be remarked that in British Patent No. 433,494 there is describeda compass in which correction is employed not by moving lubber ring I3on main frame I but by moving the azimuth gear 9 on the phantomelement 1. Our invention is equally applicable to correction appliedbetween these two members, or to correction applied elsewhere.

Returning to Figures 3 to 6, it is important to observe that ifcorrection isv applied bylrotating the lubber ring through a c rrectionangle equal to the compass error, then he two members on the compassbetween which the true course angle makes its appearance are the lubberring and the phantom element. It is for this reason that, iftransmission to repeater compasses is'used from the compass, thetransmitters are mounted on the lubber ring. Thus, the transmitter 22 ismounted on lubber ring I3 and its shaft engages by means of gearingshown as 23, 29, 25 with the azimuth gear 9. Therotation given to thetransmitter shaft is therefore proportional to true changes of courseprovided that the speed correction imparted to the lubber ring I3 isequal to the speed error of the phantom element 1 inclusive 'of theazimuth gear 9 driving the transmitter.

For the same reason, in compasses employing correction by movement ofthe lubber ring, we mount our corrector on the lubber ring whereaspreviously such correctors have been mounted on the main compass frame.rector on the lubber ring we ensure that when the ship changes course,the phantom element turns with respect to the corrector through the truechange of course angle. 'Ihe first form of our corrector is shown inFigures 3, 4, 5. In these figures the lubber ring I3 isv shown asprovided with a boss 26, in whichi's journalled a shaft 21 xed at theupper end to a disc 28 and at the lower end to a disc 29. 'I'his disccarries a circular flange 30 on which teeth are cut around the wholecircumference. 30 so formed is driven from a gear 3| of equal diameterfixed to the azimuth gear 9, the drive being by means of an idler gearon a shaft 33 journalled in the lubber ring I3. From the nature of thegearing it is evident that the disc 29 turns.

relatively tothe lubber ring through the same angle as that throughwhich the gear 3| turns relatively to the lubber ring. Since gear 3| ispart of the phantom element it follows that the angular rotation of disc29 relative to the lubber ring I3 is the true angular change of course.l

'I'he disc 2 9 extends below the gear flange 30 in a body part which ismachined through to leave two Walls 30', 30"(Fig. 5) shown dotted inFigure 4. These are slotted at 33', 34 to form a slide bearing for aslide carriage 35 from which there projects downwards a pin 36. To theupper part of the slide carriage 35 there is secured a straight rack 31with vertically cut teeth which engage with a pinion 38 on a shaft 39journalled in the shaft 21. A Y

To the upper end of shaft 39 is rigidly attached the disc 40 which iscounterbored on the vunder side so that the disc 28-ts inside it. 'I'hecylindri- By mounting the cor- The gear f.

cal surface of the disc I0 is knurled to aiord a grip and at one point atapped hole passes through it in which is located a locking screw 4Iwhich can be screwed forward so that its point `engages between tceth42cut on the disc 28. A window 43 is cut in the upper surface of the discdthrough which can be seen a circular scale M engraved on the topsurface of disc 2B. An index line 55 is engraved on fill opposite thecentre of the window.

The disc @o is the setting knob for the corrector. It is by means of itthat the corrector is set for the speed and latitude of the ship. To setthe knob a chart is first consulted: this indicates what scale numbercorresponds to any speed and latitude .of the ship. When the scalenumber is found, the locking screw @l is released, and disc d is turnedby hand until the scale number appears in the window t3 opposite theindex line t5. The locking screw il is then screwed home into engagementbetween the teeth 42 so that thereafter no relative motion is permittedbetween shafts 21 and 39 which turn together as a single shaft in thebearing in boss 26 whenever the ship changes course. Y

During the process of setting the disc 40 relative to disc Q2, the shaft21 is prevented from turning owing to the engagement of gear 30 withgear 32 which is in turn geared with the gear 3l which is held fixed bythe azimuth motor I5. Shaft 39 therefore rotates in shaft 21 and turnspinion 38 thereby driving carriage 85 along the slide bearings 33', 34,by means of rack 31. In this way the pin 36 is displaced from the centreline of shaft 39. The scale 44 and the charts of speed and latitudeaccording to which this scale is set are so made out that thedisplacement CP of pin 35 from the axis of shaft 39 is proportional Vcos L on the same scale as the distance OC of the axis of shaft 39 fromthe vertical axis of the compass is proportional to unity.

Referring to Figure 4, it is evident that the triangle OCP correspondsto the triangle OCP of Figure 2, or rather to its mirror image, for OCis a constant distance, CP is times as great, and the angle OCP is thetrue course angle (provided that the lubber ring I3 is in fact subjectedto a correctional movement relative to the compass frame l through anangle equal to the compass error).

It follows that the angle COP in Fig. 4 is equal to the compass error.

In order to move the lubber ring I3 on the compass frame i through anangle equal to the angle COP a bracket 4B is secured to the underside ofthe compass frame l, and this is slotted at-41 to 48, the slot being inavertical radial plane passing through the vertical axis of the compass.The pin P engages with this slot, so that the centre line of this slotforms the third side OP of the triangle COP of Figure 2. In this way theangle between the line OC on the lubber ring I8 and the line OP on themain frame iis caused to be the true error angle.

As the ship changes course, the phantom elemerit 1 turns relatively tothe main frame, and gear 3| drives gear 52, and thereby rotates thecrank arm CP about the centre C. The pin $5,

Y however, is always' in engagement with the slot 41 or OP, so that thelubber ring i8 is pushed round on the main frame I to provide va compassr correction in accordance with the desired formula. It will beappreciated that the distance OC on the lubber ring. the distance CP onthe adjustable rotating crank and the distance OP on the main frame. area physical embodiment of the corx'esponding lengths of Figure 2 or ofFigure 1 on a,

special scale. 4

Figures 6 and '7 show another form of our invention applied to producecompass correction in the same way by moving the lubber ring i3 on themain frame l of the same type of compass.

In this form also a physical embodiment 4of Figure 2 is set up, but thetriangle OCP'now has the point O at the circumference of the lubber ringinstead of at the compass centre, and the adjustable rotatable crank CProtates about the compass centre C instead of about a centre at thecircumference of the lubber ring. In fact this crank is formed on thecompass card and turns rigidly with it about the vertical axis of thecompass. Thereby the angle through which it turns relative to the lineOC on the lubber ring is the true course angle. In Figure 7, althoughmost of the compass card I l is broken away to show the corrector parts,it may be seen that the course angle that would be read on the cardopposite the lubber mark l2 is about 350 corresponding to a course about10 west of north. The figures have been drawn showing this course,because for the length CP chosen for the crank arm, a course angle ofabout 350 makes'the angle OPC a right angle and therefore, as is evidentfrom Figure 2, produces the maximum error angle for the length CP.

y The pin 36 of Figures 3 and 4, the distance of whose centre from theaxis C determines the crank arm length CP is replaced in the correctorof Figures 6 and '1' by a large eccentric 49 surrounding the stern 6 ofthe phantom element and the lower part of the hub I0 of the compasscard, which is rigidly attached to the stem 6. The eccentric is, ofcourse, the mechanical equivalent of the pin, being a pin whose radiusis 'larger than the crank arm radius.

The eccentric is provided with three bosses 50, and 52. A rod 53 fixedto bosses 54, 55 solid with the hub portion l0 of the compass card,passes through the bosses 5I, 50 of the eccentric and forms a slidebearing along which the eccentric ,as a whole may slide relatively tothe compass card and parallel to the axis of the rod 58. `A similar rod56 parallel to rod 53 passes through boss 52 and prevents the eccentricfrom rotating about the axis of rod 58. Rod 56 difters from rod 53,however, in being not fixed but rotatably mounted in bearings in thebosses 51, 58 on `the hub portion I0 of the compass card. Moreover, thecentral portion 59 of rod 55 is threaded and so is the boss 52, with theresult that rod 55 and boss 52 act as a screw and nut. Rotation of rod56 therefore feeds the whole eccentric 49 along slide rod 53. A knob 60above the hub portion i0 of the compass card is provided torotate therod 55 by means of bevel gearing 8l, 52.. In order to indicate thedistance CP by which the eccentric 49 is displaced from the zeroconcentric with the vertical axis C of the compass,

a member 53 is secured to the eccentric 49 and on it are cut verticalteeth to form a straight rack 54. This rack engages with a member 65shaped las part of a circular rack and solid with a vertical shaft 56joui'nalled in the hub portion I0 of the compass card. To this shaftthere is se' cured an index lever 51 marked out with a scale oflatitudes. When the eccentric is moved by the knob 65, rack 54 causesthe circular rack 55 to turn about the axis of shaft 65 and causes theindex lever 51 to rotate about this axis. The index lever in itsrotationpasses over an index plate Il marked out' in curves of knots. Thelatitude scale andthe speed curves are so drawn that, when a givenlatitude- L is set to intersect the curve for a given speed S, thedisplacement CP of eccentric 49, which has brought about thisintersection, is equal to OC multiplied by S VcosL In this way the armCP is made of the correct length relative to OC in accordance with theprinciples of our invention, so lthat there remains only to be explainedhow the correct error angle COP is picked off the device, and used toapply a correction by shifting the lubber ring I3 round the compassframe through an angle equal to triangle COP.

We first provide a member continuously directed Aalong OP even when OPturns relative to the fixed line OC on the lubber ring I3. For thispurpose we provide a pivot at O. A stud 69 is fixed into a boss 10 onthe lubber ring I3, and this forms the inner race for the 'fulcrumbearing 1I for a lever member 12. This lever is in two parts 13' and 14screwed together at 15, 16, and dowelled,

so that they pivot together as a single solid lever about the axis O ofstud 69.

The upper portion 14 is constructed as a rectangular framework which ismachined through to form a Wide slot with parallel vertical walls 11,18. 'I'hls slot corresponds to the slot 41-48 in Figure 4 since thecentre line of this slot is constrained to pass through the centre P ofthe eccentric 49 by the engagement of the eccentric in the slot. v

In order to reduce wear the eccentric 49 does not contact directly withthe walls 11, 18 of the slot. Instead, two slide blocks 19, 80 areinterposed between the eccentric and these two walls respectively. Y

Slide block 80 has a plane face resting on wall 18 and a concavecylindrical face resting on the cylindrical face of the eccentric. Slideblock 19 has also a concave cylindrical face resting on the cylindricalface of the eccentric, but it has no face in contact with the plane wall11. Instead a plate 8| loosely connected to it and sprung from itengages against this wall 11. Thereby the necessity for accuratefittings is avoided, shake is prevented, and wear is taken up. The slideblock 19 has fingers 82, 83 extending from it into slots in the slideblock an so stabinzing the mocks against rocking movementsabout axesparallel to 'I'he total eiect is that the lever 12 as a whole engageswithout shake on the eccentric 49, and is oscillated relatively to thelubber ring I3 by the eccentric as this rotates with the compass. cardround the vertical axis of the compass. The angle COP through which itoscillates is the true verror.-

angle as exhibited in Figure 2.

In order to form a guide for lever 124 as a whole for its oscillationabout the pivot O so as to prevent it from rocking or tilting, a flange84 with two lugs 85, 86, is formed on the end of the frame 14 remotefrom the pivot O. These slide over a machined surface on a bridge piece81 across two of the radial arms of the lubber ring, being held down onit by a bar 88. v

In order to rotate the lubber ring I3 on themain' frame I through anangle equal to the angle COPl through which the lever 12 oscillates onthe lubber ring, gearing is provided.

Teeth 89 are cut on the lower portion 13 of the lever 12.. Ihese engagewith a pinion- 90 on--a shaft 9| which turns in bearing 92, 93 in a boss94 on the hub of the lubber ring I3. The pinion 90 in turn engages witha gear sector 95 of the ring proportional to theangle COP and thiscauses gear sector 95 to turn relative to the lubber ring through thesame angle COP. However, since gear sector 95, is fixed to the maincompass frame, this relative movement takes eifect as a rotation of thewhole lubber ring on the compass frame through an angle equal to theangle COP, thereby providing the compass correction required.

In Figures 6 and 7 we also show how we ensure that the speed correctionprovided by our corrector remains correct when latitude damping error isalso corrected. As is well known in the art, a damping error is presentin many types of compasses, which damping error varies with latitude.

The damping error, in the type of compass described, is corrected bymoving the lubber ring, in the same Way as is the speed error.Consequently, when the correction is made, the true course angle is thatbetween the lubber ring I3 and the phantom element 1. This is the anglethat must be 'used between the lines OC and CP of the elements of thecorrector. It follows that the line OC must be xed in the lubber ring I3.

For this reason we do not apply latitude damping correction between thespeed corrector and the lubber ring as has been the practice heretofore.Instead we apply latitude damping correction between the speed correctorand the main compass frame by rotating the gear sector plate 96 withrespect to the main compass frame.

For this purpose a block 91 is fixed to the main frame I which carries ascale 98 marked out in latitudes and which forms the bearing support foran adjustment screw 99. Engaging with this screw there is a worm sectorplate |00 on which is carried a. pointer |0| moving over the scale 98 toindicate the latitude for which adjustment of the damping error is made.'Ihe scale is so marked out that the plate |00 turns about the compasscentre through the damping error angle corresponding to the latitudeindicated.

The plate |00 is rigidly connected to the plate 96 so as to position itin azimuth. In the figures the connection is shown as a broad steppedspring plate |02 which is rigid in azimuth but acts as a thrust springradially so forcing the plate |00 into engagement with the thread of theadjusting screw 99 and preventing shake.

When the pointer `|0| is set to a given latitude the gear sector 95 istherefore set round on the compass frame through an angle equal to thedamping error, and as a result the whole correction mechanism includingthe lubber ring is given a correction equal to this error. The internalangular relations of the parts of the speed correc- 'tor device itselfare, however, correct in spite of method such as by mechanical orelectrical differentials.

Many other embodiments of the invention are also possible. v

What we claim is:

1. In a correction device for gyro `compass apparatus, the combinationwith a rotatable compass member, a lubber ring member adapted forreading with said compass member, means for turning one of said memberswith respect to the other through the speed errox` correction angle ofthe compass, said means comprising an element pivoted upon said lubberring member and turnable on its pivot with respect to said lubber ringmember, a settable indemng member connected for causing the turning ofsaid element in accordance with speed and latitude, and gearingcooperable with said element for eiecting in conjunction therewith thebodily shifting of one of said members through the desired speed errorcorrection angle as said indexing member is operated 2. In a correctiondevice for gyro compass membery connected for causing the turning of 1said element, gearing cooperable with said element for effecting inconjunction therewith the bodily shifting of one of said members throughthe desired speed error correction angle as said indexing member isoperated, and means cooperating with said gearing for automaticallychanging the relative angular positions of said compass and lubber ringmembers as the course of the craft carrying the compass varies.

3. In a correction device for gym. compass apparatus, the combinationwith a rotatable compass card member, a reference member providing alubber mark adapted for reading with said rotatable card member, andmechanism for turning one of said members with respect to the otherthrough the speed error correction angle of the compass, said mechanismcomprising a tumable lever element pivoted on said reference member at aradial distance removed from the central axis of the compass a lengthcorresponding to the diurnal velocity of a point on the earths surfaceat the latitude of the craft, indexing means connected for turning saidlever element to establish a second length representative of the speedof the craft relative to the earths surface. while simultaneouslyeffecting the bodily shifting of one of said members through the properspeed error correction angle.

4. A correction device as defined in claimi, having settable meanscooperable with said gearing for effecting additional turning of saidpivoted lever element to thereby also introduce latitude damping error.

5. In a navigationalapparatus, a compass card, a lubber ring having alever member pivoted thereon, the distance between the vertical compasscard axis and the pivotal axis of said lever esltablishing a fixedlength independent of latitude and representing in a velocity triangle aside corresponding to the diurnal velocity of a point on the earthssurface at the latitude of the craft, and indexing means for turningsaid lever member to thereby establish aylength at the appropriate angleto the first length corresponding in the velocity triangle to the craftspeed divided by the' diurnal velocity of a point on the earths surfaceat the-latitude of the craft, and mechanism connected with said leverandoperable in response to movement thereof for relatively shifting saidcompass card and lubber ring through an angle corresponding to theresultant speed error correction angle determined by the direction ofthe resultant -velocity corresponding to the third side of the velocitytriangle.

6. A navigational apparatus as defined in claim 5. having a transmittermounted on said lubber ring.

7. In a. navigational apparatus for use on ships or other vehicles,having a movable compass indicator,.means associated with said compassindicator for correcting the indications thereof in accordance withchanges both in speed and latitude of such ship or other vehicle.indexing means actuated by a single manual operation for actuating saidrst mentioned means, and further means cooperable with said first namedmeans for automatically correcting the compass indications in accordancewith the movements of said compass indicator corresponding to changes incourse.

8. In a navigation apparatus for ships, a compass card, a lubber ringadjacent thereto, a c orrection device connected to a relatively fixedpart of said apparatus and ,having connections with said card and ring,said lconnections being such that said device is adapted to angularlyshift the position of said lubber ring in response to movements of saidcard, and manually operable indexing means cooperable with saidconnections for changing the relative positions of the parts of saiddevice in accordance with the velocity and latitude of such ship to varythe amplitude of such shifting.

9. A navigation apparatus as defined in claim 8, wherein said correctivedevice functions on the principle of a velocity triangle, one corner ofthe triangle being in the vertical center line of the compasscardfanother on the axis of the lubber ring connection, and the thirdcorner being adjustable eccentrically withjrespect to said first comerso as to be spaced therefrom a distance corresponding to the speed ofthe ship.

WILLIAM GEORGE HARDING. ROBERT HAYES NISBET.

